New Insights into\nthe Structure, Thermal Properties,\nand Photostability of Industrially Relevant Salts of Sorbic Acid

Potassium, sodium, and calcium salts of sorbic acid (CH<sub>3</sub>–CHCH–CHCH–COOH) are\nwidely\nused food preservatives. Despite the industrial relevance, their solid-state\nchemistry associated with photoreactivity and heat-induced transformations\nof double bonds remains misunderstood, mostly because of the lack\nof structural information. Herein, we report a comprehensive structural,\nthermal, and spectroscopic study of the above sorbates along with\npreviously unknown normal and acid ammonium sorbates for comparison.\nAlthough all of the crystal structures exhibit a similar layered motif\nand carboxylate coordination, in potassium sorbate, there is an additional\nnoncovalent interaction between K<sup>+</sup> and the C<sub>α</sub>C<sub>β</sub> bond that bestows the salt with unique\nthermal properties. In turn, only the acid ammonium sorbate has a\npreorganization for [2 + 2] photocycloaddition, as reflected by its\nfast amorphization under soft UV irradiation, opposite to the other\nsalts. The experimental results are discussed in the context of related\nmetal carboxylates and the application and analysis of the studied\nsalts in food industry.